In recent years, linear motion guide units have been built in sliding portions of various types of machines and apparatuses such as semiconductor manufacturing apparatus, machine tools, and assembling machines, and their use has been expanded. For such a linear motion guide unit, there has been demand to reduce its section height and prevent a decrease in the rigidity of the unit, which decrease would otherwise occur due to the reduced section height.
A conventional roller-type linear motion guide bearing device having an increased rigidity is disclosed in, for example, Japanese Patent Application Laid-Open No. 2006-138386. In the linear motion guide bearing device, rollers are used as rolling elements; a slider main body has padding (volume-increasing) portions provided at opposite inner corner portions thereof which face opposite corner portions of a guide rail located at widthwise opposite ends of the upper surface thereof; and the opposite corner portions of the guide rail have inclined surfaces which extend in the axial direction and which serve as volume decreasing portions which decrease the volumes of the opposite corner portions of the guide rail by an amount corresponding to the amount by which the volumes of the opposite inner corners of the slider main body are decreased by the padding (volume-increasing) portions.
A linear motion guide unit including a slider which straddles an elongated guide rail and which can slide in the longitudinal direction of the guide rail via rollers serving as rolling elements is disclosed in, for example, Japanese Patent Application Laid-Open No. 2015-64057. The slider of the linear motion guide unit includes a carriage which has a pair of raceway surfaces formed to face raceway surfaces of a guide rail and return passages extending parallel to the pair of raceway surfaces; end caps which are disposed on end surfaces of the carriage located on opposite sides thereof with respect to its sliding direction and have turnaround passages for establishing communications between upper and lower raceway passages and upper and lower return passages; and end seals disposed on end surfaces of the end caps located on the outer side thereof with respect to the sliding direction. Rollers and separators are built in such that, within the raceway passages, the end surfaces of the rollers are held by corresponding retainer plates attached to the carriage and the end caps and the rollers roll and travel, with their rolling surfaces (their cylindrical outer circumferential surfaces) being in contact with the raceway surfaces. The retainer plates are attached to the slider through use of holding bands whose opposite ends are fixed to the end caps.
Also, a guide device using roller retainers is disclosed in, for example, Japanese Patent Application Laid-Open No. 2012-2361. The disclosed guide device includes roller retainers each coupling a large number of rollers, and roller retainer holding members for holding the roller retainers. In the guide apparatus, opposite inner corner portions of the slider have inclined surfaces so as to increase the volumes of the corner portions.
In the above-described linear motion guide bearing device disclosed in Japanese Patent Application Laid-Open No. 2006-138386, when an external tensile or compressive load acts on the slider main body, the rigidity of the slider main body decreases, and the slider main body deforms such that the wing portions of the slider main body open (i.e., the distance between the wing portions of the slider main body increases), which is not preferred and is problematic. The publication discloses a measure for overcoming the above-mentioned problem. Specifically, in the linear motion guide bearing device, volume increasing portions realized by inclined surfaces are formed at the opposite inner corner portions of the slider so as to increase the volumes of the corner portions, and volume decreasing portions are formed at the corner portions of the guide rail which face the volume increasing portions. However, the linear motion guide bearing device has a problem that the overall height of the device itself is large because the inclined surfaces of the opposite inner corner portions of the slider have an inclination angle of 45°. In the guide device disclosed in Japanese Patent Application Laid-Open No. 2012-2361, which includes roller retainers and roller retainer holding members for holding the roller retainers, inclined surfaces are also formed at the opposite inner corner portions of the slider so as to increase the volumes of the corner portions. However, since the inclined surfaces of the opposite inner corner portions of the slider have an inclination angle of 45° as in the case of the linear motion guide bearing device described above, the guide device has a problem that the overall height of the device itself is large.
Incidentally, there has been demand for such a linear motion guide unit to reduce the section height of a carriage which forms a slider. In order to meet such a demand, the inventors of the present invention modified the conventional carriage such that a central portion of the carriage has a reduced thickness. In this case, however, there has occurred a phenomenon that the rigidity of shoulder portions of the carriage between the central portion and the wing portions thereof decreases, and when the carriage receives a load, the wing portions deform. Therefore, there is a technical challenge to configure a linear motion guide unit such that even when the thickness of the central portion of the carriage portion is reduced, the rigidity of the shoulder portions in the boundary regions between the central portion and the wing portions of the carriage does not decrease, and problems such as concentration of stress do not occur, whereby bending deformation of the wing portions in relation to the central portion is restrained.